#include <Servo.h>

const int trigPin = 7;
const int echoPin = 6;
const int servoPin = 9;

Servo myServo;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  myServo.attach(servoPin);
  myServo.write(0); // Start with the door closed
  Serial.begin(9600);
}

void loop() {
  long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration / 2) / 29.1;

  if (distance < 20) { // If an object is within 20 cm
    myServo.write(90); // Open the door
  } else {
    myServo.write(0); // Close the door
  }
  delay(500);
}